The present invention relates to a bus controlling technology, and in particular, to a technology effectively applicable to a method of controlling buses on a host side in an apparatus such as a magnetic disk array storage connected to or coupled with a plurality of host computers including personal computers and workstations and to a configuration of the buses.
As described in, for example, pages 103 to 107 of xe2x80x9cLatest Personal Computer Technology ""97xe2x80x9d published from Nikkei BP on Sep. 10, 1996, there have been well known a small computer system interface (SCSI) bus standard, an extended standard thereof, and the like as interfaces for connection of peripheral devices such as external storages in an information processing system including personal computers and workstations.
In the SCSI bus interface, it is commonly known that up to eight or 15 SCSI devices can be generally connected in a daisy chain configuration. However, when a failure occurs in either one of the SCSI devices in this layout of connection, there possibly exists a probability of a SCSI bus failure in many cases. Which leads to a problem of deteriorating high reliability of the entire computer system. To remove the problem, there has been introduced a technology as follows.
For example, in accordance with a technology of JP-A-8-320836, when a failure occurs in one of the SCSI devices coupled in a daisy chain, a central processing controller retries activation of the failed device. Namely, the controller operates a register in a power control circuit of a power controller to individually turn power of the failed device on or off. If the failure cannot be removed after a predetermined number retry operations, the controller turns power of the failed device off and then initializes the system again. In this technology, at a failure which cannot be removed only by turning power of the SCSI device off, it is necessary to once terminate operation of the system, for example, to replace the failed device. This consequently lowers operability of the system.
Additionally, JP-A-9-81469 describes a technology of a duplicated bus system to connect a plurality of functional modules to a control module which monitors and controls the functional modules. In the technology, the duplicated bus system includes a serial bus for the minimum monitoring and controlling operation in addition to a system bus, which is effective to identify a failed position at occurrence of a failure. However, there has not been described of any unit for separating a control module connected to the daisy chain. Namely, consideration has not been fully given to a system re-initialization after a failure associated with the bus. Furthermore, it has been generally known that when either one of the buses of the duplicated bus system is used as a backup bus at occurrence of a bus failure, usability of the system hard-ware resources is deteriorated; moreover, a degenerated bus controlling operation of the duplicated bus system causes considerable deterioration in the system performance.
In the conventional daisy chain connection, when a plurality of SCSI devices attempt to an SCSI bus access, the accesses of the respective devices are determined in accordance with SCSI arbitration priority levels thereof. Namely, a bus access wait time takes place for each SCSI device and hence the data transfer rate is lowered.
With increase in the computer system size, in the data processing speed, and in the data capacity, storage devices such as magnetic array storages are required to operate at a high speed with high reliability. In relation to the cluster layout of host computers, there has been known a method of sharing storage devices therebetween by connecting the devices via an SCSI bus in a daisy chain.
However, for a failure of a shared bus, the conventional technology has a technological problem that the failure possibly leads to an inconvenience situation in which the system cannot continue its operation.
It is therefore an object of the present invention is to provide a bus controlling technology for use in a system including a plurality of information processing apparatuses coupled via a particular bus interface to each other, the technology improving reliability of the system at occurrence of a bus failure.
Another object of is to provide a bus controlling technology for use in a system including a plurality of information processing apparatuses connected via a particular bus interface to each other, the technology improving throughput of data transfer between the information processing apparatuses.
Another object of the present invention is to provide a bus controlling technology for use in a system including a plurality of host computers coupled via a particular bus interface to particular peripheral devices, the technology improving reliability of the system at occurrence of a bus failure.
Another object of the present invention is to provide a bus controlling technology for use in a system including a plurality of host computers coupled via a particular bus interface to particular peripheral devices, the technology improving the data transfer throughput between the host computers and the peripheral devices.
To achieve the objects above in accordance with the present invention, in a second information processing apparatus including one or more controllers, each controller including a plurality of independent ports for controlling communication of information through an arbitrary bus protocol with a first arbitrary external information processing apparatus coupled via a bus interface with the second information processing apparatus and a control unit for controlling a data transfer between a plurality of ports, the control unit monitors a state of each of the ports and transmits at least a portion of a bus protocol to be executed in an arbitrary one of the ports to a bus interface of another one thereof.
Specifically, for example, a controller including a plurality of bus coupling ports includes a control unit to virtually establish a state in which the bus coupling ports seem to be physically connected in a daisy chain. The control unit includes, for example, a microprogram to logically transmit operation on a bus to ports other than a port related to the bus in a logically same controller. For each bus coupling port, there are disposed the controller and a device unit including an operator""s console to set possibility or impossibility of execution the transmission control operation above.